The invention relates generally to universal joints. More specifically, embodiments of the invention relate to ball hubs for use in universal joints and methods of manufacture.
In today""s vehicles, the steering system generally includes a common shaft, supported by a steering column, coupling a steering wheel to a steering gear assembly for transmitting directional rotation from a user to a steering geometry to provide directional control. The shaft typically passes through a vehicle firewall that separates passenger and engine compartments. To provide for various vehicle steering column designs, safety considerations and user comforts, the shaft has to navigate a complicated route necessitating two or more joints that connect the rotating shafts allowing for freedom of rotation regardless of the different angles the steering shaft experiences.
A Cardan, or yoke type universal joint, is frequently used to accomplish the transitions between steering shaft angles. This type of universal joint is common in the industry and includes two yokes and a cross shaft. Bearing surfaces couple the cross shaft to the yokes, allowing for a predetermined freedom of movement in two planes.
Gaining in popularity is the ball hub universal joint, shown in FIGS. 1 and 2, that provides for a reduction in weight, size, and NVH (Noise, Vibration and Harshness). This type of universal joint includes a first shaft 17 having at one end a ball hub 19, that is usually attached with a long pin 21 allowing for a first axis of pivotal motion. The long pin 21 passes through one side of the ball hub 19 along an equator, through the first shaft 17, and back into the ball 19. The ball 19 is received in a cup 23 that is rigidly attached to a second shaft 25. The ball hub 19 is retained in the cup 23 using two short pins 27, 27xe2x80x2 that allow for a second axis of pivotal motion orthogonal to the first axis. Each short pin 27, 27xe2x80x2 passes through the outside of the cup 23 and into the ball 19 along the equator.
For most passenger car and light truck applications, the ball hub and cup can be made from self-lubricating plastics such as Teflon(copyright), Delrin(copyright), or others, thereby obviating the need for low friction bearing surfaces between the moving parts (pins, ball and cup). However, for applications that are subjected to severe driving conditions which result in high dynamic torque loads, metal offers greater robustness and durability than most self-lubricating plastics. The metal parts need low friction load bearing surfaces.
To minimize friction and NVH in both axis of rotation, bushings are placed into the ball hub 19 pin holes where the long pin 21 and short pins 27, 27xe2x80x2 couple the first shaft 17 to the ball hub 19 and to the cup 23 as shown in FIG. 3. The bushings are typically made of a self-lubricating material. Each bushing has an associated flange surface to minimize friction between surfaces of the first shaft 17 and ball hub 19, and the ball hub 19 and cup 23. The long pin 21 bushings 29, 29xe2x80x2 locate their flange surfaces 33, 33xe2x80x2 on the interior of the ball hub 19, the short pin 27, 27xe2x80x2 bushings 31, 31xe2x80x2 locate their flange surfaces 35, 35xe2x80x2 on the exterior of the ball hub 19.
While bushing inserts solve one problem, they create a problem of their own. Depending on the design specification, the allowable rotational lash or play between the first and second shafts may be specified at a minimum. Precise, low clearance fits would therefore be required between the long 21 and short 27, 27xe2x80x2 pins and ball hub 19 to meet the lash specification of the steering shaft. Since a bushing is a removable cylindrical guide, where one low clearance fit existed between the pin and mating surface, another low clearance fit between the bushing and mating surface is created. The clearance between the three components increases rotational lash above design specifications. Further, the bushings can rotate when the joint is being exercised causing binding of the joint. This in turn increases the torque necessary to rotate the shaft while concomitantly decreasing the joint articulation.
The prior art has addressed this shortcoming by decreasing the internal diameter of the bushings such that the insertion of the pins causes the bushings to expand, reducing the clearance fit between the long 21 and short 27, 27xe2x80x2 pins, bushings 29, 29xe2x80x2, 31, 31xe2x80x2 and ball hub 19. However, during assembly, insertion of the pins can shave the inner diameter of the bushings resulting in unacceptable lash. Additionally, the bushings would not expand sufficiently to reduce clearance between the bushing and ball hub to achieve an acceptable lash.
The inventors have discovered that it would be desirable to have a low lash ball hub for use in a universal joint and methods for manufacturing, for applications such as steering column shafts that experience a high torque load. One aspect of the invention provides a universal joint hub comprising a generally spherical body having two flat areas on opposing exterior sides and at least one opening into an open body interior. The hub has two flat areas on opposing interior surfaces of the body orthogonal to the exterior flat areas and an exterior circumferential groove extending between the exterior flat areas on a given plane. Four apertures extend into the body and are positioned orthogonal to each other on the given plane with each aperture disposed in one of the flat areas. A bushing is disposed in each aperture having a face exposed to the exterior surface. A circumferential band is disposed in the circumferential groove coupling each of the bushings.
The method begins with forming a generally spherical body having two flat areas on opposing exterior sides and at least one opening into an open body interior. Forming two flat areas on opposing interior surfaces of the body, the interior flat areas orthogonal to the exterior flat areas. Forming an exterior circumferential groove extending between the exterior flat areas on a given plane and creating four apertures extending into the body and positioned orthogonal to each other on the given plane with each aperture disposed in one of the flat areas. Disposing a bushing in each of the apertures, each bushing having a face exposed to the exterior surface and disposing a circumferential band in the circumferential groove thereby coupling each of the bushings.
Other objects and advantages of the method will become apparent to those skilled in the art after reading the detailed description of the preferred embodiment.